Can you reply to migrated emails?

Answer:

Yes. Some versions of Exchange use legacy DNs as email addresses for internal delivery. Here is an example of a legacy DN email address: /o=Org/ou=Department/cn=Recipients/cn=user. This format i​s also sometimes referred to as X400 or X500 address.

Most migration solutions migrate email as-is. Any email whose recipients use the legacy DN format cannot be replied to unless the legacy DN matches Active Directory information in the new environment (which is very common). To solve this problem, MigrationWiz automatically converts legacy DNs into SMTP email addresses to ensure migrated emails can be replied to.